Lens blank blocking



Jan. 27, 1970 M. o. RUDD 3,491,439

LENS' BLANK BLOCKING Filed March 2, 1966 NVENTOR.

United States Patent 3,491,489 LENS BLANK BLOCKING Milo 0. Rudd, Fort Lauderdale, Fla., assignor to Uulvls, Inc., Fort Lauderdale, Fla., a corporation of Ohio Filed Mar. 2, 1966, Ser. No. 531,302 Int. Cl. B24]: 19/00, 1/00 U.S. Cl. 51-277 6 Claims ABSTRACT OF THE DISCLOSURE A two-piece cast block is molded on the finished side of a lens blank and includes an outer substantially annular ring and a central radially inwardly spaced substantially circular plug. Both pieces are cast substantially simultaneously and preferably from a low melting point metallic alloy. The annular ring includes an outer surface referenced to the ultimate optical center of the finished lens and a radially inner surface referenced to the ultimate mechanical center of the finished lens. The outer ring with these references is employed primarily for generating the prescribed optical surface on the unfinished side of the lens blank and then for smoothing and polishing this generated surface. The inner plug is referenced to the ultimate mechanical center and includes a horizontal alignment surface which is referenced to the ultimate horizontal axis of the finished lens, such as the segment line of a bifocal lens blank. This central plug is employed following the removal of the outer ring in mounting and aligning the lens blank in edging apparatus for forming the final edge contour of the lens.

The present invention relates to the manufacture of ophthalmic lenses and, more particularly, to blocking these lenses so that they can be processed in apparatus for generating and polishing their surfaces and finally for edge grinding the lenses according to prescription. A block, as commonly understood, is a rigid holder which is temporarily fastened to the surface of a lens for the purpose of holding and positioning the lens while it undergoes further processing.

In the course of manufacturing an ophthalmic lens through the employment of blocking of one type or another, the blocking employed during the generating, grinding, and polishing operations performed on the lens blank is generally of such large dimensional proportions that interference therewith would inevitably occur during the final edging operation. As a result, a number of approaches have been proposed to alleviate this problem, the obvious being to provide a separate block for the final edging operation. However, this requires the additional steps of marking up and/or aligning the lens and block relative thereto for eventual mutual securement. With the advent of low melting point alloy blocking materials, the inventor of the above identified parent application proposed removal of the radially outwardly disposed portions of the block that would ordinarily interfere with the final edging operations.

It is a primary object of this invention to improve upon the subject matter disclosed in the above identified parent application by providing a two-piece cast block as distinct from the one-piece cast block of that application and in which the outer portion may be independently removed from the inner portion whereupon the latter can be employed for cooperating with apparatus for introducing the final edge contour on the blank.

In accordance with an exemplary and somewhat preferred embodiment of the invention, a two-piece cast block is molded on the finished surface of a lens blank through the employment of apparatus of the type disclosed in the above identified parent application. The block includes an ice outer substantialy annular ring and a central radially inwardly spaced substantially circular plug. Both pieces are cast substantially simultaneously from the same material preferably of the type of low melting point metallic alloys commonly employed for blocking in the ophthalmic lens manufacturing field. The annular ring includes an outer surface referenced to the ultimate optical center of the finished lens and a radially inner surface referenced to the ultimate mechanical center of the finished lens. The outer ring with these references is employed primarily for generating the prescribed optical surface on the unfinished side of the lens blank and then for smoothing and polishing this generated surface. The inner plug is referenced to the ultimate mechanical center and includes a horizontal alignment surface which is referenced to the ultimate horizontal axis of the finished lens, such as the segment line of a bifocal lens blank. This central plug is employed follow-- ing the removal of the outer ring in mounting and aligning the lens blank in edging apparatus for forming the final edge contour of the lens.

Other objects and advantages will become apparent from the following detailed description which is to be taken in conjunction with the accompanying drawings illustrating a somewhat preferred embodiment of the invention and in which:

FIG. 1 is a top plan view of a bifocal lens having secured to one face thereof a two-piece cast block in accordance with the teachings of this invention;

FIG. 2 is a cross-sectional view of this lens blank and two-piece block;

FIG. 3 is a fragmentary and sectional view of a mold assembly for forming the two-piece cast block on the lens blank with the inner mold shown in a raised position about to be lowered following the start of the dispensing of the casting material;

FIG. 4 is a similar fragmentary sectional view showing the inner mold lowered into place with the discharge of the cast material having been completed;

FIG. 5 is a top plan view of the lens blank having secured thereto only the inner plug piece of the two-piece cast block following the removal of the outer annular ring;

In the drawings, a blocked lens assembly 10 is shown comprising a typical semi-finished lens blank 12 and a two-piece cast block 14. With respect to the lens blank 12, it is shown in the general condition in which it is received from the supplier by the optical laboratory. For exemplary purposes, the blank 12 may be taken to be a bifocal blank having the main portion of one index of refractionand a bifocal segment of a different index of refraction. In the blank illustrated, the front or outer surface, which would ordinarily be on the exterior of the finished spectacles, is finished to a predetermined contour, usually spherical. The rear surface will, after further processing, possess the prescribed optical surface in accordance with the necessary optical corrections for the individual eyes of the ultimate wearer of the spectacles. As previously explained, the lens blank 12 may assume one of a number of other forms and the finished lens similarly could be selected from a wide variety of lenses known to the industry.

With respect to the cast two-piece block 14, a. suitable blocking material in the nature of a low melting point alloy is initially poured in a molten state into a mold as- 3 ing of the block material, the block 14 will have incorporated thereon the desired and selected references introduced during the molding process. In this connection, an outer substantially" annular ring 16 includes an external surface 18 which serves as 'the optical center reference with the axial center line of the optical center reference containing the ultimate optical center of the finished lens. An' inner somewhat conical surface 20 serves as the mechanical center reference,the axial center line of which lccontains the ultimate mechanical center of the finished ns. An inner substantially centrally located plug 22 spaced inwardlyof the outer ring 16 constitutes the other part of block 14.: This plug 22 is formed with an outer substantially conically shaped surface 24 which serves as the mechanicalicenter reference, and an upper cavity or kef. slot 26 having its azimuthal position in fixed relation to the horizontal position or axis reference of the finished lens. In the ease of a bifocal lens, the horizontal axis reference will be substantially parallel to the top segment line of the bifocal segment.

The block 14 is provided with surfaces" for cooperating with the various chucking means to be engaged. Thus, a pair of diametrically opposed key slots 28 is formed in the exterior of the outer annular ring 16 and cooperates with the chucking'rneans of a toric generator designed to generate the prescribed optical surface. The substantially radial key slot 30 cooperates with the chucking means of smoothing and polishing apparatus. As will be more fully explored below, theslot 26 is adapted to cooperate with chucking means of edging apparatus followingthe remo al of the outer annular ring 16 for purposes of forming the final edge contour ef the blank according to prescription.

i Turning now to the exemplary. mold assembly 32 adapted to advantageously form the block 14, it should be initially understood that the above identified parentzapplication contains a completed disclosure of molding apparatus of which the mold assembly 32 forms a part; and where the present invention departs structurally and operationally from the apparatus of that application, the present disclosure will endeavor to supply the pertinent details. Thus, the technician positions the block forming mold assembly 32 on the front or convex surface of the blank 12. This assembly is defined by an external mold 34 and an inner mold 36. The outer mold 34 serves to contour the block 14 with an optical axis reference while being aligned azimuthally with respect to the lens blank 12 according to the prescribed cylinder axis. The inner mold 36 forms the mechanical center reference and also serves to contour a further cylinder axis reference slot 30 and the horizontal reference slot 26 aligned with the horizontal reference axis.

In the case of a bifocal lens blank, the optical center is first locatedwith respect to the segment and then the mechanical center is loaded with respect to the optical center. The horizontal axis is maintained without change regardless of all other changes in the position of the inner die 36 during the blocking operation. As explained, this horizontal reference will be parallel to the desired horizontal meridian of the finished lens, such as would be determined by the segment line of a bifocal lens blank. Initially, and as depicted in FIG. 3, the inner mold 36 is in a raised position at the start of the pouring of the molding or casting material from the valve controlled pouring spout 38. Immediately thereafter, the inner mold 36 is lowered into position such that the inner cavity thereof will trap a suflicient amount of the casting material therein for purposes of producing the inner plug 22. The excess casting material will have been forced radially outwardly and to facilitate the passage of excess casting material, where desirable or necessary, the inner mold 36 may be provided with a very small passage 40. Upon completion of the molding cycle and setting of the block 14, the inner mold 36 is retracted and the lens and block assembly eventually ejected from the mold assembly 32.

The lens blank and block assembly 19 is now mounted in an edge grinding or contouring apparatus which operates to form a peripheral contour edge on the blank 12, one suitable type of which is shown in FIG. 5. The chucking means of this apparatus is adapted to engage with the conical inner surface 20 of the outer ring 16 as well as the key slot 26 of the inner plug 22, thus; the desired contour is formed on the blank 12 referenced to both the mechanical center and the horizontal axis of the finished lens."

Following this contouring operation, during which the area of the blank is shaped to a balanced condition around the ultimate mechanical center and'the size of the semifinished blank is significantly reduced, the assembly 10 is mounted in a conventional toric or spherical surface generating machine.-The optical center reference surface 18,

together' with the key slots 28 therein, are employed in mounting and locating the assembly 10 in the chucking means bf the generator. The slots 28 WilL'nnder these circumstances, serve to relate the assembly 10 to the prescribed cylinde'raxis angle when mounted in the generator so that the generated toric surface will be properly oriented on the blank.

Once the toric surface is generated on the blank 12, it is ground and polished using conventional surfacing machines. The chucking means of these machines is adapted to engage with the mechanical center reference surface 20, together, with the key slot 30. In this manner, the desired surface is ground and polished about the mechanical center, and in a balanced condition, while assuring accuracy of cylinder axis. a I

Next the final edge contour is formed and for such purposes, the outer annular ring 16 is removed, as shown in FIG. 5. This may be easily accomplished by placing the outer ring 16 between the :jaws of a vice, pliers or other suitable pressure applying tool adapted to squeeze the ring which has the effect of cleanly removing the ring 16 from the lens blank 12 independent of the central plug 22. Following the removal of the outer annular ring 16, the assembly 10 is placed in conventional final edging apparatus. The chucking means of this apparatus is adapted to engage with the mechanical center reference surface 24 and key slot 26 of the central plug 22. The ultimate edge contour is formed on the finished lens about the mechanical center while referenced to the horizontal alignment; and the lens is thereby prepared to be mounted in a spectacle frame of predetermined dimensions. Prior to this, however, the plug 22 is removed in a suitable manner. In the case of the low melting point alloy materials mentioned in the above, this may be simply done by applying heat or by immersing the assembly 10 in sufiiciently hot water or other suitable liquid, thereby freeing the central plug from the finished lens blank.

Thus, among others, the several aforenoted objects and advantages are most effectively attained. Although a single somewhat preferred embodiment has been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be determined by that of the appended claims.

I claim:

1. A blocked lens blank unit comprising a lens blank having at least one optically finished lens surface, and a cast two-piece lens block both pieces of which are formed of low melting point alloy material and adhered to the finished lens blank surface for temporarily supporting the lens blank during processing of the lens blank, one piece being in the form of a spaced radially outwardly disposed annular ring, said ring having a radially inner and outer surface, said outer surface being an optical center reference. surface aligned with the ultimate optical center of the finished lens, said radially inner surface being a mechanical center reference surface aligned with the ultimate mechanical center of the finished lens, said outer surface having keying means for cooperating with chucking means of a generator for forming the prescribed optical surface on the unfinished side of said lens and the inner surface having keying means for cooperating with chucking means of smoothing and polishing apparatus, the other piece being a plug aligned with the ultimate mechanical center of the finished lens and having a horizontal alignment surface referenced according to the ultimate horizontal alignment of the finished lens, and said annular ring being so constructed and arranged to be removable from the finished side of said lens independent of said plug and said plug having aligning and gripping surfaces for cooperating with apparatus for forming the final edge contour of the finished lens on said blank with respect to the mechanical center and horizontal alignment surfaces on the plug.

2. The invention in accordance with claim 1 wherein the horizontal alignment reference is provided by a relatively raised and recessed portion of the plug.

3. A method of blocking a semi-finished lens blank to be finished into an ophthalmic lens according to prescription, comprising the steps of: supporting a semi-finished lens blank in a predetermined position; determining the locating of the ultimate optical center of the finished lens on said blank; attaching an outer annular ring to the finished surface of the semi-finished lens blank having an optical center reference surface aligned with the ultimate optical center of the finished lens and a mechanical center reference surface aligned with the ultimate mechanical center of the finished lens; simultaneously attaching a central plug spaced radially inwardly of the outer ring and structurally independent thereof, the plug being aligned with respect to the ultimate mechanical center of the finished lens and having a horizontal alignment surface referenced to the ultimate horizontal alignment of the finished lens; the outer annular ring and central plug being attached to the finished surface of the semi-finished lens blank by simultaneously casting in place the outer annular ring and central plug on the lens blank through the deployment of a first and second mold, both said outer annular ring and central plug being cast of the same low melting point alloy material; the first mold having a center, the second mold having a center, the central axes of said molds containing the ultimate optical and mechanical centers with one of the molds having a horizontal alignment reference forming surface, and removing the molds following casting of the outer annular ring and central plug on the lens blank.

4. A method of producing an ophthalmic lens according to prescription comprising the steps of: supporting a semifinished lens blank in a predetermined position; determining the location of the ultimate optical center of the finished lens on said blank; attaching an outer annular ring to the finished surface of the semi-finished lens blank having an optical center reference surface aligned with the ultimate optical center of the finished lens and a mechanical center reference surface aligned with the ultimate mechanical center of the finished lens; simultaneously attaching a central plug spaced radially inwardly of the outer ring and structurally independent thereof, the plug being aligned with respect to the ultimate mechanical center of the finished lens and having a horizontal alignment surface referenced to the ultimate horizontal alignment of the finished lens; forming the prescribed optical surface on the unfinished side of the lens blank with reference to the optical center reference surface related to the ultimate optical center by employing the outer annular ring; finishing the thus formed prescribed optical surface by employing the outer annular ring; removing the outer annular ring from the lens blank; forming the final edge contour of the finished lens with respect to the mechanical center and the required horizontal alignment of the lens by employing the central plug.

5. The invention in accordance with claim 4 wherein the outer annular ring has a cylinder axis reference surface referenced according to the prescribed cylinder axis and utilizing the cylinder axis reference surface in forming the prescribed optical surface.

6. A method of blocking a semi-finished lens blank to be finished into an ophthalmic lens according to prescription, comprising the steps of: supporting a semi-finished lens blank in a predetermined position; determining the locating of the ultimate optical center of the finished lens on said blank; attaching an outer annular ring to the finished surface of the semi-finished lens blank having an optical center reference surface aligned with the ultimate optical center of the finished lens and a mechanical center reference surface aligned with the ultimate mechanical center of the finished lens; simultaneously attaching a central plug spaced radially inwardly of the outer ring and structurally independent thereof the plug being aligned with respect to the ultimate mechanical center of the finished lens and having a horizontal alignment surface referenced to the ultimate horizontal alignment of the finished lens; the outer annular ring and central plug being simultaneously cast in place on the lens blank by positioning a first mold into relative engagement with the blank, the first mold having a center, positioning a second mold in spaced relation relative to the blank, the second mold having a center, the central axes of said molds containing the ultimate optical and mechanical centers with one of said molds having a horizontal alignment reference forming surface, then introducing casting material into the first mold; subsequently shifting the second mold into engagement with the lens blank to capture a predetermined quantity of the casting material, and removing said molds following setting of the casting material.

References Cited UNITED STATES PATENTS 1,911,153 5/1933 Hill 51-277 X 3,226,887 1/1966 Rudd et al. 51277 3,192,676 7/1965 Buckminster 51277 X ANDREW R. JUHASZ, Primary Examiner GIL WEIDENFIELD, Assistant Examiner US. Cl. X.R. 51284 

